Hard coating for cutting tool

ABSTRACT

Provided is a hard film for a cutting tool formed on a surface of a base material, the hard film being comprised of a nano multi-layered structure comprising a thin layer A, a thin layer B, a thin layer C and a thin layer D or a structure in which the nano multi-layered structure is repeatedly stacked at least twice, wherein the thin layer A is comprised of Ti 1-x Al x N (0.5≦x≦0.7); the thin layer B is comprised of Al 1-y-z Ti y Cr z N (0.3≦y≦0.6 and 0&lt;z≦0.3); the thin layer B is comprised of MeN (where Me is Nb or V); and the thin layer D is comprised of Al 1-a-b Ti a Si b N (0.3≦a≦0.7 and 0&lt;b&lt;0.1).

TECHNICAL FIELD

The present invention relates to a hard film formed on a hard basematerial such as a hard metal, a cermet, a high-speed steel, an endmill, a drill, a cNB or the like that is used in a cutting tool, andmore particularly, to a hard film for a cutting tool configured with anano multi-layered structure including a thin layer A, a thin layer B, athin layer C and a thin layer D or with a repeatedly stacked structurethereof, thus improving all of abrasion resistance, lubrication,toughness and oxidation resistance compared to an existing multi-layeredthin film structure.

BACKGROUND ART

As the industry gradually advances toward fineness, speedup and massproduction, it is required to improve cutting performance and life cycleof a cutting tool. Especially, since high heat of 900° C. or more islocally generated on a front end of the cutting tool rubbing with aworkpiece in a rapid cutting of a workpiece having a high hardness and acutting of a difficult-to-cut material having a low thermalconductivity, life cycle of the cutting tool may be improved by forminga hard film having excellent oxidation resistance and abrasionresistance on a cutting surface of the cutting tool.

In order to improve the cutting performance and life cycle, asingle-layered hard film including TiN, Al₂O₃, TiAlN, AlTiN, AlCrN orthe like having abrasion resistance, oxidation resistance, impactresistance and the like, or a multi-layered hard film in which thesingle-layered hard films are stacked in two layers or more, is formedon a hard base material such as a hard metal, a cermet, a high speedsteel, an end mill, a drill, or the like to cope with demands for thehigh hardness workpiece and the difficult-to-cut material.

Recently, the hardness of the workpiece is gradually increased, and ademand for processing of a difficult-to-cut material having a lowthermal conductivity and severely fused on a tool is also increased.Especially, since stainless steel, heat-resistant alloy steel, ductilecast iron and the like have a low thermal conductance compared togeneral steels, cutting heat is not emitted due to chips in a cuttingand heat is concentrated on a cutting edge portion of the cutting tool,abrasion, seizure and exfoliation phenomena are easily generated on thecutting edge of the cutting tool due to a chemical reaction between thecutting tool and the workpiece, and life cycle of the cutting tool israpidly reduced.

Therefore, only with the single layered or multi-layered structureshaving a composition described above, it becomes more and more difficultto cope with a demand for a cutting tool for the cutting of such adifficult-to-be cut material and ductile cast iron, which are requiredto evenly have characteristics such as excellent abrasion resistance,oxidation resistance and lubrication.

Therefore, trials improving the cutting performance are recentlyincreased through a method for regularly and repeatedly stacking atleast two thin films having a nano level that are different in materialproperty.

For example, Korea Patent No. 876366 discloses a thin film structure inwhich a lower layer is deposited on an insert, an end mill, a drill or acermet which is a hard metal tool through a physical vapor deposition,in order to improve an adhesion force and align the orientation ofcrystal grains in the direction of (200) plane, a (Ti,Al)N multi-layeredthin film which is a middle layer is continuously deposited in order toimprove impact resistance and chipping resistance, and a top layer whichis comprised of TiAlN or AlTiSiN, is constituted by layer A, layer B,layer C and layer D and has a structure in which layer A, layer B, layerC and layer D are alternately stacked, is formed to improve the abrasionresistance and oxidation resistance of the top layer.

While the abrasion resistance and oxidation resistance may be improvedthrough the multi-layered structure as described above, development of ahard film having a novel structure is required in order to evenlyimprove various characteristics such as abrasion resistance, impactresistance (toughness) and chipping resistance required for the cutting.

DISCLOSURE Technical Problem

The present invention provides a hard film for a cutting tool by whichabrasion resistance, lubrication, toughness (impact resistance) andoxidation resistance are generally improved.

Technical Solution

According to an embodiment of the present invention, a hard film for acutting tool is formed on a surface of a base material, the hard filmbeing comprised of a nano multi-layered structure including a thin layerA, a thin layer B, a thin layer C and a thin layer D or a structure inwhich the nano multi-layered structure is repeatedly stacked at leasttwice, wherein the thin layer A is comprised of Ti_(1-x)Al_(x)N(0.5≦x≦0.7); the thin layer B is comprised of Al_(1-y-z)Ti_(y)Cr_(z)N(0.3≦y≦0.6 and 0<z≦0.3); the thin layer B is comprised of MeN (where Meis Nb or V); and the thin layer D is comprised ofAl_(1-a-b)Ti_(a)Si_(b)N (0.3≦a≦0.7 and 0<b<0.1).

According to another embodiment of the present invention, it ispreferable that the nano multi-layered structure be formed bysequentially stacking the thin layer A, the thin layer B, the thin layerC and the thin layer D on the base material.

According to another embodiment of the present invention, it ispreferable that each of the thin layer A, the thin layer B, the thinlayer C and the thin layer D have an average thickness of 3 nm to 50 nm.

According to another embodiment of the present invention, it ispreferable that each of the thin layer A, the thin layer B, the thinlayer C and the thin layer D have an average thickness of 20 nm to 40nm.

According to another embodiment of the present invention, it ispreferable that the hard film have an average thickness of 1 μm to 20μm.

According to another embodiment of the present invention, it ispreferable that the hard film have a degradation hardness not less than35 GPa when degradation-treated at a temperature of 900° C. for 30minutes.

Advantageous Effects

According to a hard film for a cutting tool of the present invention,since various characteristics required for a hard film for a cuttingtool, such as abrasion resistance, lubricant, toughness, chippingresistance, and oxidation resistance, may be evenly improved through arepeated stacking of a nano multi-layered structure formed bysequentially stacking a Ti and Al composite nitride layer commonlyhaving excellent abrasion resistance and an adhesion to a base material,an Al, Ti and Cr composite nitride layer having excellent lubricant, anNb or V composite nitride layer having excellent toughness and chippingresistance and also having improved lubricant under a high temperatureenvironment, and an Al, Ti and Si composite nitride layer havingexcellent oxidation resistance, the hard film may be suitably used inprocessing of a difficult-to-cut material.

That is, in the hard film for the cutting tool of the present invention,thin layers for reinforcing abrasion resistance, lubricant, toughness,and oxidation resistance of each thin layer are periodically andrepeatedly stacked to maximize the functions of the respective thinlayers, thus capable of harmoniously improving abrasion resistance,lubricant, toughness, and oxidation resistance required for cutting thedifficult-to-cut material.

DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic cross-sectional view illustrating a structure of ahard film for a cutting tool according to the present invention.

BEST MODE

Hereinafter, embodiments of the present invention will be described withreference to the accompanying drawings to fully explain the presentinvention in such a manner that it may easily be carried out by a personwith ordinary skill in the art (hereinafter, referred as an ordinaryskilled person) to which the present invention pertains. The presentinvention may, however, be embodied in different forms and should not beconstrued as limited to the embodiments set forth herein. Also, in thefigures, the dimensions of layers and regions are exaggerated forclarity of illustration.

FIG. 1 is a schematic cross-sectional view illustrating a structure of ahard film for a cutting tool according to the present invention. Asillustrated in FIG. 1, a thin film for a cutting tool has a structure inwhich a thin layer A, a thin layer B, a thin layer and a thin layer Dare sequentially stacked on a base material to form a nano multi-layeredstructure, and the nano multi-layered structure is repeatedly stackedtwice or more.

The thin layer A is a thin layer aiming to mainly improve abrasionresistance and hardness, and has a composition that is comprised ofTi_(1-x)Al_(x)N (0.5≦x≦0.7).

In the thin layer A, when an Al content is less than 0.5, since Alhaving an atomic radius smaller than that of Ti, is substituted, andthus a solid solution amount of Al is decreased, abrasion resistance andhardness of the thin film are reduced, and since TiO₂ oxide is easilyformed under a high temperature environment in a cutting, a Ti atom inthe thin film may be diffused to the outside to incur the hightemperature hardness reduction due the depletion of the Ti atom, andwhen an Al content is more than 0.7, since a phase having a hexagonal B4structure is formed to reduce abrasion resistance and life cycle of atool, it is preferable that the Al content be 0.5 or more and 0.7 orless.

The thin layer B is a thin layer aiming to mainly improve lubricant, andhas a composition that is comprised of Al_(1-y-z)Ti_(y)Cr_(z)N(0.3≦y≦0.6 and 0<z≦0.3).

In the thin layer B, it is preferable that a Ti content be 0.3 or moreand 0.6 or less, and the reason is because when a Ti content is lessthan 0.3, a phase having a hexagonal M4 structure is formed to increasebrittleness, to reduce abrasion resistance and to decrease life cycle ofa tool, and when a Ti content is more than 0.6, Al having an atomicradius smaller than that of Ti is substituted to decrease the solidsolution amount of Ti atom and hardness and abrasion resistance of athin film, and TiO₂ oxide is easily formed under a high temperatureenvironment in a cutting, so a Ti atom in the thin film may be diffusedto the outside to incur the high temperature hardness reduction due thedepletion of the Ti atom.

Also, the thin layer B contains 0.3 or less of Cr, and when a Cr contentis 0.3, lubricant may be remarkably improved. However, when a Cr contentis more than 0.3, a coarse thin film structure is formed andconcurrently, if the tool is exposed to a high temperature environmentin a cutting, segregation of Cr₂N is formed to reduce abrasionresistance and life cycle of the tool. Accordingly, it is preferablethat the Cr content be limited to less than 0.3.

The thin layer C is a thin layer aiming to mainly improve toughness andchipping resistance, and is comprised of NbN or Vn basically having highfracture toughness and chipping resistance. Such a thin layer C isphase-changed to V₂O₅ or Nb₂O₅ in a high temperature work environment sothat a lubricant characteristic is improved, and the improvement inlubricant characteristic prevents a film from being exfoliated togetherwith a workpiece to more improve chipping resistance and toughness.

Like this, the thin layer C comprised of NbN or VN forms a multi-layerin a nano level together with a thin film having a different component,and thus allows a hard film for a cutting tool to have evenly and highlybalanced characteristics in various terms of toughness, chippingresistance, lubricant and abrasion resistance.

The thin layer D is a thin layer aiming to mainly improve oxidationresistance and hardness, and a detailed composition thereof is comprisedof Al_(1-a-b)Ti_(a)Si_(b)N (0.3≦a≦0.7 and 0<b<0.1).

In the thin layer D, it is preferable that a Ti content be 0.3 to 0.7,and the reason is that when the Ti content is less than 0.3, a phasehaving a hexagonal M4 structure is formed to increase brittleness and toreduce abrasion resistance and life cycle, and when the Ti content ismore than 0.7, Al having an atomic radius smaller than that of Ti issubstituted to reduce the solid solution amount of Ti, thus reducinghardness and abrasion resistance of a thin film, and TiO₂ oxide iseasily formed under a high temperature environment in a cutting, so thata Ti atom in the thin film may be diffused to the outside to incur thehigh temperature hardness reduction due the depletion of the Ti atom.

Also, the thin layer D contains less than 0.1 of Si, and the reason isbecause when Si is added in a small amount (a moderate amount) of 0.1, anon-crystalline Si₃N₄ phase is formed along a grain boundary of acrystalline AlTiN phase to refine grains of the crystalline AlTiN phase,so that hardness and abrasion are preferably improved. Also, anon-crystalline Si₃N₄ phase forms a SiO₂ oxide to play role inpreventing outdiffusion of an internal atom into the outside in a hightemperature cutting, thus improving the life cycle of the cutting tool.

However, in the thin layer D, when a Si content is more than 0.1, thenon-crystalline Si₃N₄ phase is increased to reduce hardness, and a grainrefinement effect of the crystalline AlTiN phase is lowered to reduceabrasion resistance, so, this is not preferable.

Meanwhile, it is preferable that the thin layer A, the thin layer B, thethin layer C, and the thin layer D have an average thickness of 3 nm to50 nm.

This is because as the period of a nano multi-layered structure isdecreased, occurrence and movement of dislocation are suppressed, andthus a thin film is reinforced, and when the thickness of the thin filmis as thin as less more 3 nm, a mixing zone is formed by interdiffusionbetween two layers to reduce hardness and an elastic modulus while aboundary between the nano multi-layers for suppressing the occurrenceand movement of the dislocation becomes unclear, so it is preferablethat the thin film be formed in a thickness not less than 3 nm, and whenthe thickness is more than 50 nm, the occurrence and movement of thedislocation are easier, so that hardness and an elastic modulus arereduced and also coherency strain energy is reduced by formation ofmisfit dislocation, so that a reinforcement effect reduction phenomenonis accompanied, which is not preferable.

Also, it has been confirmed through an experiment in which onlythicknesses of the layers are changed that since an excellent grainboundary reinforcement effect for suppressing movement of dislocationmay be obtained through plastic deformation when thicknesses of the thinlayer A, the thin layer B, the thin layer C, and the thin layer D are ina range of 20 nm to 40 nm, this thickness range is most preferable.

In preferable Example of the present invention, while the thin layer A,the thin layer B, the thin layer C, and the thin layer D aresequentially stacked so as to form the nano multi-layered structurehaving the order of A-B-C-D, the realizing method is not limitedthereto, and may rather be realized in various types such as A-D-C-B,B-A-D-C, D-A-C-B and the like.

However, when the hard film for the cutting tool according to thepresent invention is realized in a stack structure in which thin filmhardness (and a residual stress) of each layer influencing abrasionresistance and toughness of each thin film is periodically oscillated,since abrasion resistance and toughness representing characteristicsrelative to each other may be improved at the same time, it is mostpreferable that the thin film layers be realized in a nano multi-layeredstructure having the order of A-B-C-D.

Like this, it is most preferable that the thin film for the cutting toolaccording to the present invention having a nano multi-layered structureor a structure in which the nano multi-layered structure is repeatedlystacked at least twice, have an average thickness of 1 μm to 20 μm.

As described above, the present invention forms a nano multi-layeredstructure through a combination of a TiAlN, AlTiCrN and AlTiSiN basedthin layer and an NbN or VN thin layer, and is characterized in evenlyimproving abrasion resistance, lubricant, toughness, chipping resistanceand oxidation resistance with respect to an entire hard film.

EXAMPLES

In the present invention, a hard film was coated on a surface of a hardbase material of WC-10 wt % Co by using an arc ion plating method thatis a physical vapor deposition (PVD), the hard base material including acermet, high speed steel, an end mill, drill or the like. In thecoating, a TiAl target, a AlTiCr target, an Nb or V target and an AlTiSitarget were used with respect to a thin layer A, a thin layer B, a thinlayer C and a thin layer D, respectively. An initial pressure wasreduced to 8.5×10⁻⁵ Torr or less, and N₂ was introduced as a reactiongas. A gas pressure for coating was 30 mTorr or less and preferably 20mTorr or less, a coating temperature was 400° C. to 550° C., and asubstrate bias voltage was applied in −20 V to −150 V in a coating. Ofcourse, the coating condition may be different from that of Example ofthe present invention according to an equipment characteristic andcondition.

In Example of the present invention, a TiAlN film that is an abrasionresistance layer, an AlTiCr film that is a lubricant layer, an NbN filmor a VN film that is a toughness layer, and AlTiSin film that is anoxidation resistance layer were sequentially stacked at an averagethickness of 28 nm to 31 nm to form a nano multi-layered structure, andthen such a nano multi layered structure was repeatedly formed tomanufacture a hard film for a cutting tool having a total thickness of3.4 μm to 3.6 μm according to Example embodiment of the presentinvention.

Meanwhile, if necessary, it goes without saying that various types ofthin films may be additionally formed on a hard film for a cutting toolformed according to Example of the present invention.

Also, since a hard film for a cutting tool according to Example of thepresent invention is formed by using a physical vapor deposition (PVD),a thin film thickness may be formed up to 20 μm.

The following Table 1 shows each of a composition, a target compositionratio, a thin film average thickness, a total film thickness and a stackstructure with respect to a hard film for a cutting tool according toExample of the present invention.

TABLE 1 Structure of Hard Film Thin Film Exam- Nano Multi-layeredAverage Total Film ple Structure (Target Thickness Thickness Stack No.Composition Ratio) (nm) (μm) Structure 1 TiAlN(5:5)/ 31 3.5 QuinaryAlTiCrN(54:38:8)/ A/B/C/D Nano NbN/AlTiSiN(58:37:5) Multi-layer 2TiAlN(5:5)/ 30 3.4 Quinary AlTiCrN(54:38:8)/ A/B/C/D NanoVN/AlTiSiN(58:37:5) Multi-layer 3 TiAlN(5:5)/ 30 3.6 QuinaryAlTiCrN(4:3:3)/ A/B/C/D Nano NbN/AlTiSiN(58:37:5) Multi-layer 4TiAlN(5:5)/ 31 3.4 Quinary AlTiCrN(4:3:3)/ A/B/C/D NanoVN/AlTiSiN(58:37:5) Multi-layer 5 AlTiN(7:3)/ 31 3.5 QuinaryAlTiCrN(54:38:8)/ A/B/C/D Nano NbN/AlTiSiN(58:37:5) Multi-layer 6AlTiN(7:3)/ 30 3.4 Quinary AlTiCrN(54:38:8)/ A/B/C/D NanoVN/AlTiSiN(58:37:5) Multi-layer 7 AlTiN(7:3)/ 30 3.5 QuinaryAlTiCrN(4:3:3)/ A/B/C/D Nano NbN/AlTiSiN(58:37:5) Multi-layer 8AlTiN(7:3)/ 28 3.4 Quinary AlTiCrN(4:3:3)/ A/B/C/D NanoVN/AlTiSiN(58:37:5) Multi-layer

Also, in order to relatively evaluate characteristics of hard films fora cutting tool formed according to Examples of the present invention,hard films having almost the same thickness as Examples of the presentinvention were formed in thin film structures shown the following Table2 on a base material of WC-10 wt % Co equal to that of Examples of thepresent invention.

TABLE 2 Structure of Hard Film Average Total Comparative Nano Multi-Thickness Film Example layered of Thin Thickness Stack No. StructureFilm (nm) (μm) Structure 1 TiAlN(5:5)/ 30 3.5 Ternary AlTiCrN(54:38:8)/A/B/C Nano TiN Multi-Layer 2 TiAlN(5:5)/ 30 3.5 Ternary AlTiCrN(4:3:3)/A/B/C Nano TiN Multi-Layer 3 AlTiN(7:3)/ 31 3.4 TernaryAlTiCrN(54:38:8)/ A/B/C Nano TiN Multi-Layer 4 AlTiN(7:3)/ 31 3.6Ternary AlTiCrN(4:3:3)/ A/B/C Nano TiN Multi-Layer 5 AlTiN(7:3)/ 30 3.6Quaternary AlCrN(7:3)/ A/B/C Nano AlTiSiN(58:37:5) Multi-Layer 6TiAlN(5:5)/ 31 3.7 Quaternary AlCrN(7:3)/ A/B/C Nano AlTiSiN(58:37:5)Multi-Layer 7 AlTiN(7:3)/ 31 3.8 Quaternary AlTiCrN(54:38:8)/ A/B/C NanoAlTiSiN(58:37:5) Multi Layer 8 TiAlN(5:5)/ 30 3.5 QuaternaryAlTiCrN(54:38:8)/ A/B/C Nano AlTiSiN(58:37:5) Multi-Layer 9 TiAlN(5:5)/30 3.4 Quaternary AlTiCrN(54:38:8)/ A/B/C Nano NbN Multi-Layer 10TiAlN(5:5)/ 29 3.4 Quaternary AlTiCrN(4:3:3)/ A/B/C Nano VN Multi-Layer11 AlTiN(7:3)/ 28 3.6 Quaternary AlTiCrN(4:3:3)/ A/B/C Nano NbNMulti-Layer 12 AlTiN(7:3)/ 29 3.3 Quaternary AlTiCrN(4:3:3)/ A/B/C NanoVN Multi-Layer 13 TiAlN(5:5)/ 31 3.5 Quaternary AlTiCrN(54:38:8)/ A/B/CNano NbN/AlTiN(67:33) Multi-Layer 14 TiAlN(5:5)/ 32 3.6 QuaternaryAlTiCrN(54:38:8)/ A/B/C Nano VN/AlTiN(67:33) Multi-Layer 15 TiAlN(5:5)/33 3.8 Quaternary AlCrN(7:3)/TiN/ A/B/C Nano AlTiSiN(58:37:5)Multi-Layer

As confirmed in Table 2, in Comparative Examples 1 to 4, a TiAlN film oran AlTiN film, an AlTiCrN film and a TiN film were sequentially stackedin an A/B/C stack structure at an average thickness of 30 nm to 31 nm toform hard films each having a total thickness of 3.4 μm to 3.6 μm, inComparative Examples 5 to 8, a TiAlN film or an AlTiN film, an AlCrNfilm or an AlTiCrN film and an AlTiSiN film were sequentially stacked inan A/B/C stack structure at an average thickness of 30 nm to 31 nm toform hard films each having a total thickness of 3.5 μm to 3.8 μm, andin Comparative Examples 9 to 12, a TiAlN film or an AlTiN film, anAlTiCrN film and an NbN film or a VN film were sequentially stacked inan A/B/C stack structure at an average thickness of 28 nm to 30 nm toform hard films each having a total thickness of 3.3 μm to 3.6 μm, and,these hard films are to confirm a cutting performance differenceaccording to a nano multi layer composition (where some thin films areexcepted or the hard films are formed of thin films having a generalcomposition, such as a TiN film or an AlCrN film) difference and a stackstructure difference from hard films for a cutting tool according toExamples of the present invention.

Also, in Comparative Examples 13 to 15, a TiAlN film, an AlTiCrN film oran AlCrN film, an NbN film, a VN film or a TiN film, and an AlTiN filmor an AlTiSiN film were sequentially stacked in an A/B/C/D stackstructure at an average thickness of 31 nm to 33 nm to form hard filmseach having a total thickness of 3.5 μm to 3.8 μm, and, theses hardfilms are to confirm a cutting performance difference according to anano multi layer composition (where some thin films are formed of adifferent general composition) difference from hard films for a cuttingtool according to Examples of the present invention.

The following Tables 3 and 4 show measurement results of realcompositions of thin films constituting each layer measured by using anenergy dispersive X-ray spectrometer (EDX) after hard films for acutting tool according to Examples of the present invention andComparative Examples were formed.

TABLE 3 Nano Multi-layered Structure Example (Target Composition ThinFilm Composition (EDX, at %) No. Ratio) Al Ti Cr Nb V Si N 1TiAlN(5:5)/AlTiCrN(54:38:8)/ 23.9 18.4 1.2 14.8 0.7 41NbN/AlTiSiN(58:37:5) 2 TiAlN(5:5)/AlTiCrN(54:38:8)/ 22.1 17.1 1.1 13.70.7 45.4 VN/AlTiSiN(58:37:5) 3 TiAlN(5:5)/AlTiCrN(4:3:3)/ 20.1 15.9 4.113.6 0.7 45. NbN/AlTiSiN(58:37:5) 4 TiAlN(5:5)/AlTiCrN(4:3:3)/ 20.2 164.1 13.7 0.7 45.4 VN/AlTiSiN(58:37:5) 5 AlTiN(7:3)/AlTiCrN(54:38:8)/24.2 14 1.1 13.3 0.7 46.8 NbN/AlTiSiN(58:37:5) 6AlTiN(7:3)/AlTiCrN(54:38:8)/ 24.9 14.4 1.1 13.7 0.7 45.2VN/AlTiSiN(58:37:5) 7 AlTiN(7:3)/AlTiCrN(4:3:3)/ 23.1 13.3 4.1 13.8 0.745 NbN/AlTiSiN(58:37:5) 8 AlTiN(7:3)/AlTiCrN(4:3:3)/ 23.5 13.6 4.2 140.7 44.1 VN/AlTiSiN(58:37:5)

TABLE 4 Nano Multi-layered Comparative Structure Example (TargetComposition Thin Film Composition (EDX, at %) No. Ratio) Al Ti Cr Nb VSi N 1 TiAlN(5:5)/AlTiCrN(54:38:8)/ 19.4 35.1 1.5 44 TiN 2TiAlN(5:5)/AlTiCrN(4:3:3)/ 16.8 33.6 5.6 44 TiN 3AlTiN(7:3)/AlTiCrN(54:38:8)/ 22.7 30.8 1.5 45 TiN 4AlTiN(7:3)/AlTiCrN(4:3:3)/ 20 29.1 5.5 45.5 TiN 5 AlTiN(7:3)/AlCrN(7:3)/36.3 12.3 5.5 0.9 45 AlTiSiN(58:37:5) 6 TiAlN(5:5)/AlCrN(7:3)/ 33.2 16.25.6 0.9 44 AlTiSiN(58:37:5) 7 AlTiN(7:3)/AlTiCrN(54:38:8)/ 34.5 19.9 1.50.9 43.2 AlTiSiN(58:37:5) 8 TiAlN(5:5)/AlTiCrN(54:38:8)/ 29.1 22.5 1.40.9 46.1 AlTiSiN(58:37:5) 9 TiAlN(5:5)/AlTiCrN(54:38:8)/ 18.4 15.5 1.417.7 47 NbN 10 TiAlN(5:5)/AlTiCrN(4:3:3)/ 15.8 14.1 5.3 17.6 47.2 VN 11AlTiN(7:3)/AlTiCrN(4:3:3)/ 20.2 11 5.5 18.3 45 NbN 12AlTiN(7:3)/AlTiCrN(4:3:3)/ 20 10.9 5.5 18.2 45.4 VN 13TiAlN(5:5)/AlTiCrN(54:38:8)/ 24.3 17.2 1.1 14.2 43.2 NbN/AlTiN(67:33) 14TiAlN(5:5)/AlTiCrN(54:38:8)/ 24.8 17.5 1.2 14.5 42 VN/AlTiN(67:33) 15TiAlN(5:5)/AlCrN(7:3)/ 25.1 26.4 4.2 0.7 43.5 TiN/AlTiSiN(58:37:5)

As confirmed in Table 3 described above, the formed hard films for acutting tool have real compositions that are somewhat different fromtarget compositions, but almost similar to the target compositions.

Evaluation of Room Temperature Hardness, Degradation Hardness, FrictionCoefficient and Crack Length

In order to compare and evaluate Examples 1 to 8 of the presentinvention and Comparative Examples 1 to 15 formed as described above, amicrohardness test was performed using a Fisher scope (model name“HP100C-XYP”; Germany HELMUT FISCHER GMBH, ISO14577), and roomtemperature hardness directly after forming hard films and degradationhardness after a high temperature degradation treatment at a temperatureof 900° C. for 30 minutes were measured, respectively.

Such a microhardness test was performed under conditions of a load of 30mN, an unload of 30 mN, a load time of 10 sec., and a creep time of 5sec.

Also, in order to evaluate a friction characteristic of the hard films,a sliding distance (60 revolutions of a ball (where a material is SiN₄,a diameter is 4 mm, and hardness is HV50g1600)) was measured through aball-on-disc test by using a CETR UMT-2 micro-tribometer. At this time,the friction characteristic evaluation was performed under conditions ofa temperature of 20° C. to 25° C., a relative humidity of 50% to 60%,and a rotation speed of 318 rpm (10 m/min).

Also, in order to evaluate toughness (crack resistance) of the hardfilms, a length of a crack generated on the hard film was measured byapplying a diamond pressure mark having a load of 30 kgf.

Measurement results of room temperature hardness, degradation hardness,a friction coefficient and a crack length obtained with respect toExamples 1 to 8 of the present invention and Comparative Examples 1 to15 are shown in Tables 5 and 6, respectively.

TABLE 5 Room Nano Multi-layered Temperature Degradation Friction CrackExample Structure (Target Hardness Hardness Coefficient Length No.Composition Ratio) (GPa) GPa) (COF) (μm) 1 TiAlN(5:5)/AlTiCrN(54:38:8)/38 36.2 0.4 42 NbN/AlTiSiN(58:37:5) 2 TiAlN(5:5)/AlTiCrN(54:38:8)/ 37.236 0.42 43 VN/AlTiSiN(58:37:5) 3 TiAlN(5:5)/AlTiCrN(4:3:3)/ 36.9 35.90.35 41 NbN/AlTiSiN(58:37:5) 4 TiAlN(5:5)/AlTiCrN(4:3:3)/ 37 35.5 0.3844 VN/AlTiSiN(58:37:5) 5 AlTiN(7:3)/AlTiCrN(54:38:8)/ 38.5 36.7 0.41 45NbN/AlTiSiN(58:37:5) 6 AlTiN(7:3)/AlTiCrN(54:38:8)/ 38.4 36.9 0.42 45VN/AlTiSiN(58:37:5) 7 AlTiN(7:3)/AlTiCrN(4:3:3)/ 38.1 37.1 0.39 41NbN/AlTiSiN(58:37:5) 8 AlTiN(7:3)/AlTiCrN(4:3:3)/ 37.9 36.5 0.39 42VN/AlTiSiN(58:37:5)

TABLE 6 Room Comparative Nano Multi-layered Temperature DegradationFriction Crack Example Structure (Target Hardness Hardness CoefficientLength No. Composition Ratio) (GPa) GPa) (COF) (μm) 1TiAlN(5:5)/AlTiCrN(54:38:8)/TiN 34 28 0.6 43 2TiAlN(5:5)/AlTiCrN(4:3:3)/TiN 33.5 27 0.42 49 3AlTiN(7:3)/AlTiCrN(54:38:8)/TiN 35.8 28.4 0.58 44 4AlTiN(7:3)/AlTiCrN(4:3:3)/TiN 34.2 26.8 0.48 45 5 AlTiN(7:3)/AlCrN(7:3)/36.8 34.5 0.5 47 AlTiSiN(58:37:5) 6 TiAlN(5:5)/AlCrN(7:3)/ 36.4 34.10.54 44 AlTiSiN(58:37:5) 7 AlTiN(7:3)/AlTiCrN(54:38:8)/ 36.5 34.4 0.5642 AlTiSiN(58:37:5) 8 TiAlN(5:5)/AlTiCrN(54:38:8)/ 35.9 34.1 0.59 42AlTiSiN(58:37:5) 9 TiAlN(5:5)/AlTiCrN(54:38:8)/NbN 35.8 30.1 0.45 52 10TiAlN(5:5)/AlTiCrN(4:3:3)/VN 35 31.5 0.4 49 11AlTiN(7:3)/AlTiCrN(4:3:3)/NbN 34.9 30 0.42 48 12AlTiN(7:3)/AlTiCrN(4:3:3)/VN 35.1 30.3 0.39 44 13TiAlN(5:5)/AlTiCrN(54:38:8)/ 37.5 32.5 0.54 50 NbN/AlTiN(67:33) 14TiAlN(5:5)/AlTiCrN(54:38:8)/ 38 32 0.56 49 VN/AlTiN(67:33) 15TiAlN(5:5)/AlCrN(7:3)/ 37.4 31.8 0.53 51 TiN/AlTiSiN(58:37:5)

As confirmed in Tables 5 and 6, in comparison between hard films ofComparative Examples 1 to 12 and hard films for a cutting tool accordingto Examples of the present invention, the hard films of the comparativeexamples except for some of thin films having nano multi-layeredcompositions or formed of a general composition such as a TiN film or anAlCrN film and having a stack structure of an A/B/C, have roomtemperature hardness of 33.5 GPa to 36.8 GPa which is low compared toroom temperature hardness of 36.9 GPa to 38.5 GPa of Examples to 8 ofthe present invention, and especially, have degradation hardness of 26.8GPa to 34.5 GPa which is very low compared to degradation hardness of35.5 GPa to 37.1 GPa of Examples 1 to 8 of the present invention, andtherefore, it may be confirmed that hardness is remarkably reduced undera high temperature degradation environment.

Also, it may be confirmed that most of Comparative Examples 1 to 12 havea friction coefficient of 0.4 to 0.6 except for a friction coefficientof 0.39 of Comparative Example 12, which is high compared to a frictioncoefficient of 0.35 to 0.42 of Examples 1 to 8 of the present invention.

Furthermore, Comparative Examples 1 to 12 have a crack length of 42 μmto 52 μm, whereas Examples 1 to 8 of the present invention have a cracklength of 41 μm to 45 μm all of which are short within 45 μm, andtherefore, it has been confirmed that the hard films for a cutting toolaccording to Examples of the present invention are excellent intoughness.

Meanwhile, in comparison between hard films of Comparative Examples 13to 15 and hard films for a cutting tool according to Examples of thepresent invention, the hard films of Comparative Examples 13 to 15 havethe same stack structure of an A/B/C/D as the hard films of Examples ofthe present invention, but it has been confirmed that the hard films inwhich some of thin films having the nano multi-layered compositions areformed of a general composition such as a TiN film or an AlCrN film,have room temperature hardness of 37.4 GPa to GPa which is somewhatsimilar to room temperature hardness of 36.9 GPa to 38.5 GPa of Examples1 to 8 of the present invention, but have degradation hardness of 31.8GPa to 32.5 GPa which is still considerably low compared to degradationhardness of 35.5 GPa to 37.1 GPa of Examples 1 to 8 of the presentinvention.

Also, Comparative Examples 13 and 15 have a friction coefficient of 0.52to 0.56 which is very high compared to a friction coefficient of 0.35 to0.42 of Examples 1 to 8 of the present invention, and thus it has beenshown that lubricant thereof is very low compared to Examples 1 to 8 ofthe present invention.

Furthermore, Comparative Examples 13 and 15 have a crack length of 49 μmto 51 μm which is very long compared to a crack length of 41 μm to 45 μmof Examples 1 to 8 of the present invention, and thus it has beenconfirmed that the hard films for a cutting tool according to Examplesof the present invention are very excellent in toughness.

It may be seen that the hard films of Examples 1 to of the presentinvention has toughness, lubricant (a friction coefficient) andtoughness (crack resistance) evenly improved compared to the hard filmsof Comparative Examples 1 to 15 from evaluations with respect tophysical properties of the hard films described above.

Evaluation of Abrasion Resistance

In order to evaluate cutting performance when the hard films of Examples1 to 8 of the present invention and Comparative Examples 1 to 15 areused in a cutting requiring especially abrasion resistance, a millingcutting test was performed under conditions of a workpiece: alloy steel(SCM440, a milling), Sample Type No. SPKN1504EDSR (ISO), cutting speed:200 m/min, cutting feed rate: 0.2 mm/tooth, and cutting depth: 2 mm, andresults are respectively shown in the following Tables 7 and 8

TABLE 7 Cutting Nano Multi-layered Life cycle Example Structure (Target(cutting Life cycle No. Composition Ratio) length. M) End Factor 1TiAlN(5:5)/AlTiCrN(54:38:8)/ 18 normal NbN/AlTiSiN(58:37:5) abrasion 2TiAlN(5:5)/AlTiCrN(54:38:8)/ 17.5 normal VN/AlTiSiN(58:37:5) abrasion 3TiAlN(5:5)/AlTiCrN(4:3:3)/ 17.5 normal NbN/AlTiSiN(58:37:5) abrasion 4TiAlN(5:5)/AlTiCrN(4:3:3)/ 17.8 normal VN/AlTiSiN(58:37:5) abrasion 5AlTiN(7:3)/AlTiCrN(54:38:8)/ 18.2 normal NbN/AlTiSiN(58:37:5) abrasion 6AlTiN(7:3)/AlTiCrN(54:38:8)/ 18.5 normal VN/AlTiSiN(58:37:5) abrasion 7AlTiN(7:3)/AlTiCrN(4:3:3)/ 17.5 normal NbN/AlTiSiN(58:37:5) abrasion 8AlTiN(7:3)/AlTiCrN(4:3:3)/ 17.5 normal VN/AlTiSiN(58:37:5) abrasion

TABLE 8 Cutting Comparative Nano Multi-layered Life cycle ExampleStructure (Target (cutting Life cycle No. Composition Ratio) length. M)End Factor 1 TiAlN(5:5)/AlTiCrN(54:38:8)/ 9 Chipping TiN 2TiAlN(5:5)/AlTiCrN(4:3:3)/ 9.5 excessive TiN abrasion 3AlTiN(7:3)/AlTiCrN(54:38:8)/ 11 excessive TiN abrasion 4AlTiN(7:3)/AlTiCrN(4:3:3)/ 11 excessive TiN abrasion 5AlTiN(7:3)/AlCrN(7:3)/ 12 chipping AlTiSiN(58:37:5) 6TiAlN(5:5)/AlCrN(7:3)/ 12.5 chipping AlTiSiN(58:37:5) 7AlTiN(7:3)/AlTiCrN(54:38:8)/ 13 normal AlTiSiN(58:37:5) abrasion 8TiAlN(5:5)/AlTiCrN(54:38:8)/ 12.5 normal AlTiSiN(58:37:5) abrasion 9TiAlN(5:5)/AlTiCrN(54:38:8)/ 12 excessive NbN abrasion 10TiAlN(5:5)/AlTiCrN(4:3:3)/VN 11.5 excessive abrasion 11AlTiN(7:3)/AlTiCrN(4:3:3)/NbN 11 excessive abrasion 12AlTiN(7:3)/AlTiCrN(4:3:3)/VN 12 excessive abrasion 13TiAlN(5:5)/AlTiCrN(54:38:8)/ 15 normal NbN/AlTiN(67:33) abrasion 14TiAlN(5:5)/AlTiCrN(54:38:8)/ 16.2 normal VN/AlTiN(67:33) abrasion 15TiAlN(5:5)/AlCrN(7:3)/ 16 normal TiN/AlTiSiN(58:37:5) abrasion

As confirmed in Tables 7 and 8, Examples 1 to 8 of the present inventionhave cutting life of 17.5 m to 18.5 m of which all is 17.5 m or more,and a life cycle end factor corresponding to normal abrasion, however,it may be confirmed that in comparison between the hard films ofComparative Examples 1 to 12 and the hard films for a cutting toolaccording to Examples of the present invention, the hard films ofComparative Example except for some of thin films having nanomulti-layered compositions or formed of a general composition such as aTiN film or an AlCrN film and having a stack structure of an A/B/C, havenot ended their life cycle through normal abrasion but have ended thelife cycle through chipping or excessive abrasion except for ComparativeExamples 7 and 8, and have a cutting life cycle of only 9 m to 13 m evenwhen Comparative Examples 7 and 8 are included. Thus, it may beconfirmed that the abrasion resistance of Comparative Examples isremarkably low.

Also, it has been shown that Comparative Examples 13 to 15 having thesimilar stack structure of an A/B/C/D to Examples of the presentinvention but some of which thin films having the nano multi-layeredcompositions is formed of a general composition such as a TiN film or anAlCrN film, have ended their life cycle through normal abrasion, buthave cutting life time of 15 m to 16.2 m which is low compared to thelife cycle of 17.5 m to 18.5 m of Examples 1 to 8 of the presentinvention.

Therefore, it is confirmed that the hard films of Examples 1 to 8 of thepresent invention have an excellent abrasion resistance characteristic.

Evaluation of Toughness (Impact Resistance)

In order to evaluate cutting performance when hard films of Examples 1to 8 of the present invention and Comparative Examples 1 to 15 are usedin a cutting condition requiring especially, toughness (impactresistance), milling processing impact resistance cutting performanceevaluation (interrupted evaluation) was performed under conditions of aworkpiece: alloy steel (SCM440, alloy steel 3 line diaphragm millingprocessing), Sample Type No. SPKN1504EDSR (ISO), cutting speed: 200m/min, cutting feed rate: 0.2 mm/tooth, and cutting depth: 2 mm, theevaluation was performed until a fracture of an insert coated with ahard film, and the results are shown in the following Tables 9 and 10.

TABLE 9 Nano Multi-layered Cutting Life Example Structure (Target cycle(cutting No. Composition Ratio) length. M) 1TiAlN(5:5)/AlTiCrN(54:38:8)/ 13 NbN/AlTiSiN(58:37:5) 2TiAlN(5:5)/AlTiCrN(54:38:8)/ 10.5 VN/AlTiSiN(58:37:5) 3TiAlN(5:5)/AlTiCrN(4:3:3)/ 11 NbN/AlTiSiN(58:37:5) 4TiAlN(5:5)/AlTiCrN(4:3:3)/ 11.2 VN/AlTiSiN(58:37:5) 5AlTiN(7:3)/AlTiCrN(54:38:8)/ 10.7 NbN/AlTiSiN(58:37:5) 6AlTiN(7:3)/AlTiCrN(54:38:8)/ 10.5 VN/AlTiSiN(58:37:5) 7AlTiN(7:3)/AlTiCrN(4:3:3)/ 11.5 NbN/AlTiSiN(58:37:5) 8AlTiN(7:3)/AlTiCrN(4:3:3)/ 12 VN/AlTiSiN(58:37:5)

TABLE 9 Comparative Nano Multi-layered Cutting Life Example Structure(Target cycle (cutting No. Composition Ratio) length. M) 1TiAlN(5:5)/AlTiCrN(54:38:8)/TiN 8 2 TiAlN(5:5)/AlTiCrN(4:3:3)/TiN 8.5 3AlTiN(7:3)/AlTiCrN(54:38:8)/TiN 8.5 4 AlTiN(7:3)/AlTiCrN(4:3:3)/TiN 8.55 AlTiN(7:3)/AlCrN(7:3)/AlTiSiN(58:37:5) 9 6TiAlN(5:5)/AlCrN(7:3)/AlTiSiN(58:37:5) 9.5 7AlTiN(7:3)/AlTiCrN(54:38:8)/ 8 AlTiSiN(58:37:5) 8TiAlN(5:5)/AlTiCrN(54:38:8)/ 8.5 AlTiSiN(58:37:5) 9TiAlN(5:5)/AlTiCrN(54:38:8)/NbN 10 10 TiAlN(5:5)/AlTiCrN(4:3:3)/VN 10.511 AlTiN(7:3)/AlTiCrN(4:3:3)/NbN 11 12 AlTiN(7:3)/AlTiCrN(4:3:3)/VN 10.513 TiAlN(5:5)/AlTiCrN(54:38:8)/ 9 NbN/AlTiN(67:33) 14TiAlN(5:5)/AlTiCrN(54:38:8)/ 10 VN/AlTiN(67:33) 15TiAlN(5:5)/AlCrN(7:3)/ 9 TiN/AlTiSiN(58:37:5)

As confirmed in Table 9 and 10, Examples 1 to 8 of the present inventionhave a cutting life cycle of 10.5 m to 13 m, of which all is 10.5 m ormore and is even 13 m, however, Comparative Examples 1 to 15 have acutting life cycle of 8 m to 10.5 m, of which all is 10.5 m or less.Thus, the hard films according to Examples of the present invention showexcellent impact resistant.

Evaluation of Comprehensive Cutting Performance

Generally, since a drilling has a cutting speed which is slow comparedto a milling, and is performed under a wet condition, lubricant (seizureresistance) and chipping resistance are very important. In order tocomprehensively evaluate lubricant, chipping resistance, abrasionresistance and toughness according to hard films of Examples 1 to 8 ofthe present invention and Comparative Examples 1 to 15, a drillingperformance cutting evaluation was performed under conditions of aworkpiece: carbon steel (SCM440, a carbon steel drilling), a Sample TypeNo. SPMT07T208/XOMT07T205 9504EDSR (indexable drill insert, 20Φ-5D), acutting speed: 200 m/min, a cutting feed rate: 0.1 mm/tooth, and acutting depth: 90 mm ((penetration), and the results is shown thefollowing Tables 11 and 12.

TABLE 11 Nano Multi-layered Cutting Life Example Structure (Target cycle(hole: Life cycle No. Composition Ratio) 20Φ-90 mm) End Factor 1TiAlN(5:5)/AlTiCrN(54:38:8)/ 256 normal NbN/AlTiSiN(58:37:5) abrasion 2TiAlN(5:5)/AlTiCrN(54:38:8)/ 256 normal VN/AlTiSiN(58:37:5) abrasion 3TiAlN(5:5)/AlTiCrN(4:3:3)/ 256 normal NbN/AlTiSiN(58:37:5) abrasion 4TiAlN(5:5)/AlTiCrN(4:3:3)/ 256 normal VN/AlTiSiN(58:37:5) abrasion 5AlTiN(7:3)/AlTiCrN(54:38:8)/ 256 normal NbN/AlTiSiN(58:37:5) abrasion 6AlTiN(7:3)/AlTiCrN(54:38:8)/ 256 normal VN/AlTiSiN(58:37:5) abrasion 7AlTiN(7:3)/AlTiCrN(4:3:3)/ 256 normal NbN/AlTiSiN(58:37:5) abrasion 8AlTiN(7:3)/AlTiCrN(4:3:3)/ 256 normal VN/AlTiSiN(58:37:5) abrasion

TABLE 12 Comparative Nano Multi-layered Cutting Life Example Structure(Target cycle (hole: Life cycle No. Composition Ratio) 20Φ-90 mm) EndFactor 1 TiAlN(5:5)/ 52 seizure/ AlTiCrN(54:38:8)/TiN chipping 2TiAlN(5:5)/ 52 excessive AlTiCrN(4:3:3)/TiN abrasion 3 AlTiN(7:3)/ 104seizure/ AlTiCrN(54:38:8)/TiN chipping 4 AlTiN(7:3)/ 52 excessiveAlTiCrN(4:3:3)/TiN abrasion 5 AlTiN(7:3)/AlCrN(7:3)/ 156 chippingAlTiSiN(58:37:5) 6 TiAlN(5:5)/AlCrN(7:3)/ 208 chipping AlTiSiN(58:37:5)7 AlTiN(7:3)/ 208 chipping AlTiCrN(54:38:8)/ AlTiSiN(58:37:5) 8TiAlN(5:5)/ 208 chipping AlTiCrN(54:38:8)/ AlTiSiN(58:37:5) 9TiAlN(5:5)/ 232 excessive AlTiCrN(54:38:8)/NbN abrasion 10 TiAlN(5:5)/156 excessive AlTiCrN(4:3:3)/VN abrasion 11 AlTiN(7:3)/ 156 excessiveAlTiCrN(4:3:3)/NbN abrasion 12 AlTiN(7:3)/ 156 excessiveAlTiCrN(4:3:3)/VN abrasion 13 TiAlN(5:5)/ 232 excessiveAlTiCrN(54:38:8)/ abrasion NbN/AlTiN(67:33) 14 TiAlN(5:5)/ 256 normalAlTiCrN(54:38:8)/ abrasion VN/AlTiN(67:33) 15 TiAlN(5:5)/ 232 excessiveAlCrN(7:3)/TiN/ abrasion AlTiSiN(58:37:5)

From the results of Tables 11 and 12, it is shown that the cutting toolson which the hard films of Examples 1 to 8 of the present invention areformed, have a life cycle which is considerably high compared toComparative Examples 1 to 15. Especially, it is shown that all ofComparative Example 1 to 15 except for Comparative Example 14 have endedtheir life cycle through seizure/chipping or excessive abrasion. Thus,in a comprehensive cutting performance evaluation, the hard films ofExamples 1 to 8 of the present invention show very excellentperformance.

It has been confirmed that a nano multi-layered structure formed bysequentially stacking a Ti and Al composite nitride layer havingexcellent abrasion resistance, an Al, Ti and Cr composite nitride layerhaving excellent lubricant, an Nb or V composite nitride layer havingexcellent toughness and chipping resistance and an Al, Ti and Sicomposite nitride layer having excellent oxidation resistance may evenlyimprove various characteristics required for a hard film for a cuttingtool, such as abrasion resistance, lubricant, toughness, chippingresistance, and oxidation resistance to be suitably used in a cuttingtool for a difficult-to-cut material.

While only detailed Examples of the present invention has beenparticularly shown and described, it will be apparent to those skilledin the art that the detailed description may be amended or modifiedwithout departing from the spirit and scope of the present invention,and it will be reasonable that all modifications and amendments belongto the following claims.

1. A hard film for a cutting tool formed on a surface of a basematerial, the hard film being comprised of a nano multi-layeredstructure comprising a thin layer A, a thin layer B, a thin layer C anda thin layer D or a structure in which the nano multi-layered structureis repeatedly stacked at least twice, wherein the thin layer A iscomprised of Ti1−xAlxN (0.5≦x≦0.7); the thin layer B is comprised ofAl1−y−zTiyCrzN (0.3≦y≦0.6 and 0<z≦0.3); the thin layer B is comprised ofMeN (where Me is Nb or V); and the thin layer D is comprised ofAl1−a−bTiaSibN (0.3≦a≦0.7 and 0<b<0.1).
 2. The hard film of claim 1,wherein the nano multi-layered structure is formed by sequentiallystacking the thin layer A, the thin layer B, the thin layer C and thethin layer D on the base material.
 3. The hard film of claim 1, whereineach of the thin layer A, the thin layer B, the thin layer C and thethin layer D has an average thickness of 3 nm to 50 nm.
 4. The hard filmof claim 1, wherein each of the thin layer A, the thin layer B, the thinlayer C and the thin layer D has an average thickness of 20 nm to 40 nm.5. The hard film of claim 1, wherein the hard film has an averagethickness of 1 μm to 20 μm.
 6. The hard film of claim 1, wherein thehard film has a degradation hardness not less than 35 GPa whendegradation-treated at a temperature of 900° C. for 30 minutes.
 7. Thehard film of claim 2, wherein each of the thin layer A, the thin layerB, the thin layer C and the thin layer D has an average thickness of 3nm to 50 nm.
 8. The hard film of claim 2, wherein each of the thin layerA, the thin layer B, the thin layer C and the thin layer D has anaverage thickness of 20 nm to 40 nm.
 9. The hard film of claim 2,wherein the hard film has an average thickness of 1 μm to 20 μm.
 10. Thehard film of claim 2, wherein the hard film has a degradation hardnessnot less than 35 GPa when degradation-treated at a temperature of 900°C. for 30 minutes.